1. Field of the Invention
The present invention relates to an X-ray shield grating, a manufacturing method therefor, and an X-ray imaging apparatus.
2. Description of the Related Art
X-ray phase contrast imaging is a method of obtaining a phase image of a test object by detecting a phase shift of X rays. X-ray phase contrast imaging includes a method using Talbot interference. A method in which X-ray phase contrast imaging is performed using Talbot interference method is hereinafter referred to as an X-ray Talbot interference method.
FIG. 7 illustrates an exemplary structure of an imaging apparatus using the X-ray Talbot interference method. The imaging apparatus using the X-ray Talbot interference method generally includes an X-ray source 8 for emitting spatially coherent X rays, a diffraction grating 10 for periodically modulating phase of the X rays, an X-ray shield grating 11 in which shielding portions and transmitting portions of the X rays are periodically arranged, and a detector 12 for detecting the X rays.
First, a principle of the Talbot interference method is described in brief. When spatially coherent X rays are diffracted by the diffraction grating 10, an interference pattern referred to as a self-image is formed. When a test object 9 is disposed between the X-ray source 8 and the diffraction grating 10, X rays emitted from the X-ray source 8 are refracted by the test object 9. The X rays refracted by the test object 9 are diffracted by the diffraction grating 10. By detecting a self-image formed by the diffraction, a phase image of the test object 9 may be obtained. However, a period of the self-image formed here is smaller than a resolution of the detector 12. Therefore, the X-ray shield grating 11 in which the shielding portions for shielding against X rays and the transmitting portions for transmitting X rays are periodically arranged is disposed at a place at which the self-image is formed, and moiré is produced by overlaying the X-ray shield grating 11 on the self-image. Then, information on the phase shift of the X rays due to the test object 9 may be observed as the moiré by the detector 12.
In order to observe the moiré, it is necessary that the shielding portions of the X-ray shield grating 11 sufficiently shield against the X rays. In order to sufficiently shield against the X rays, thickness of the shielding portions need be large. However, the shielding portions need be arranged with a period of several micrometers, and thus, it is generally difficult to manufacture an X-ray shield grating having the shielding portions of large thickness.
Accordingly, various methods of manufacturing an X-ray shield grating have been proposed. For example, in Microelectronic Engineering, Volume 84 (2007), 1172-1177, a Si structure having a period twice as long as that of the X-ray shield grating is manufactured, and, by plating the Si structure with gold, an X-ray shield grating having a desired period is obtained.